The overall goal of the proposed research is to investigate possible auditory bases of speech trading relations and of phonetic universals involving covariation of acoustic cues. In general, a phonological contrast (e.g., the voicing distinction in medial stops) is realized by a multiplicity of acoustic correlates, and these correlates tend to be rather uniform across languages, often approximating the status of phonetic universals. Their universality has typically prompted phoneticians to seek explanations based on physical or physiological constraints on speech production. Correspondingly, some theorists have argued that phonetic trading relations (where the perception of one acoustic-phonetic dimension is affected by the setting of another acoustic parameter) result primarily from the listener's tacit knowledge of the regularities of speech production and their acoustic consequences. We offer the alternative hypothesis that may, perhaps most, cue- covariation universals and phonetic trading relations are based on properties of the auditory system. We suggest that acoustic correlates of a phonological contrast covary as they do across languages because speech communities tend to select cues that have mutually reinforcing auditory effects. To evaluate this auditory hypothesis, our strategy will be to demonstrate a given trading relation between acoustic dimensions that signal a phonological contrast and then to determine whether the same type of trading relation exists for analogous acoustic dimensions in nonspeech stimuli. We will apply this strategy to several different phonological contrasts; the voiced-voiceless distinction in initial stops, the voiced-voiceless distinction in medial stops and fricatives, and the stop-glide distinction. The aim in each case is to make a detailed comparison between speech and analogous non-speech versions of a given trading relation. In addition to testing human subjects, several experiments will investigate the perception of trading relations in a nonhuman species--Japanese quail. A computer model of the auditory periphery will be used to evaluate possible auditory bases of trading relations.